1. Technical Field
This invention relates to packaging memory cards, such as flash or ROM memory cards.
2. Related Art
A recent global spate of portable electronic devices such as computers, electronic toys, PDAs, cameras, smart phones, digital recorders, pagers, and such has spawned a concomitant need for compact, removable data storage components. One response to this demand has been development of so-called xe2x80x9cmemory cards.xe2x80x9d Typically, a memory card contains at least one or more semiconductor memory chips within a standardized enclosure that has connectors thereon for electrical connection to external circuitry. Examples of these include so-called xe2x80x9cPC Cardsxe2x80x9d and xe2x80x9cMultiMediaCardsxe2x80x9d made in accordance with standards promulgated by such trade associations as Personal Computer Memory Card International Association (xe2x80x9cPCMCIAxe2x80x9d) and MultiMediaCard Association (xe2x80x9cMMCAxe2x80x9d), respectively.
An exemplary embodiment of such a memory card, namely, a Multimedia-Card 10, is illustrated in top plan, cross-sectional side elevation, and bottom plan views of FIGS. 1-3, respectively. Card 10 illustrated has standardized dimensions of 32 mm long X 24 mm wide X 1.4 mm thick, and typically includes a memory capacity of 2 to 32 megabits (xe2x80x9cMBxe2x80x9d) of memory, which is accessed through seven contacts 22 located on a bottom surface of card 10 using, e.g., a standard serial port interface (xe2x80x9cSPIxe2x80x9d) interface. A simple chamfer 30 on one corner of card 10 prevents incorrect insertion of card 10 into a connector in a host device.
Memory card 10 comprises a rectangular substrate 12, such as a printed circuit board (xe2x80x9cPCBxe2x80x9d), and one or more semiconductor memory dies or xe2x80x9cchipsxe2x80x9d 14 mounted on and electrically connected thereto using, e.g., a layer 16 of adhesive and conventional wire bonds 18, respectively. Surface mounting passive components 20, e.g., resistors, may also be mounted on and connected to substrate 12. Contacts 22 are connected through substrate 12 to memory circuits defined by foregoing components and serve as input-output terminals of card 10.
When components 14, 20 have been mounted on and connected to substrate 12, chip 14 is protectively encapsulated by a xe2x80x9cglob-toppingxe2x80x9d process. A glob 24 of a viscous encapsulant is dispensed onto a top surface of chip 14, allowed to flow over its sides to said surface of substrate 12, and cured to form a protective envelope over chip 14. An external cover or housing 26 (shown by dotted outline in FIG. 1) of thin sheet metal or plastic is installed over substrate 12 assembly by embedding said top surface of assembly in a bed 28 of an adhesive contained in housing 26.
While said foregoing method provides a useable memory product, it is always desirable in a rapidly evolving market such as this to develop new fabrication methods that simplify a product, reduce its costs, and enhance its functionality.
This invention provides methods for making a memory card, e.g., a MultiMediaCard, that eliminate a need for an external housing and a separate encapsulation step, and that enables more memory to be packaged in a same size of card.
In one of said methods, a substrate having opposite first and second surfaces is provided. A memory die, or chip, is mounted on and electrically connected to said first surface of said substrate, e.g., by wire bonding. Said second surface of said substrate is attached to a first surface of a flat carrier sheet, e.g., an adhesive tape. In one embodiment, a mold is placed on said first surface of said carrier sheet such that said chip and said first surface of said substrate are enclosed in a cavity defined by said mold and said carrier sheet. Said chip and said first surface of said substrate are encapsulated in a monolithic body of hardened plastic, e.g., by injecting a fluid plastic, such as a filled liquid epoxy resin, into said cavity and curing said resin to harden same. Completed cards are then detached from said carrier sheet for use.
Said methods eliminate a need for an external housing on said card and a separate chip encapsulation step. These enable a reduction in card height, or incorporation of more memory chips in a card with a standardized height using diestacking techniques. Said methods are well adapted to volume production techniques.